It allows monitoring code and sync the files that need to be changed with a remote server. This works more efficiently than libnotify and faster than vagrant auto rsync.

Not just for PHP, HTML and JavaScript, but especially good is SQL inspection and auto-completion of tables and fields. You can see at a glance, that your DB structure is in sync with your code.

PhpStorm has two types of autocompletion: structural completion and word expansion.
Structural autocompletion makes predictions based on its understanding of PHP, while the latter tries to predict the word currently being typed based on previously typed words. Word expansion also works in comments and docstrings and it's similar to vim's omnicompletion.
Both types of autocompletion work extremely well, have little to no problems and are quite fast even when loading suggestions on the go.

PhpStorm is clearly being developed continually, which gives confidence that it will be available for some time and is not abandonware.

Supports Twig and Laravel's Blade (among others). Technically the later is part of a framework which Phpstorm supports but I've seen IDEs (e.g. Netbeans) with Laravel support but no blade support so it does deserve a notable mention.

Quickly rename classes, methods, and variables used across multiple files in the project.

Lots of plugins from JetBrains and the community are available, from useful things like support for Docker, Vagrant, Angular, Vue.js and more useless (but fun) like a nyan cat progress bar.

The database tab, while not perfect, provides all the tools you need for daily usage. You always have your DB overview on the side (you can hide it when not needed).

Supports Symfony2 (including Twig and Doctrine), Yii frameworks, and Laravel.

Currently costs £78 but does not seem to offer much more than some free counterparts.

Has built-in support for Xdebug including remote debugging.